The replacement of utility lines is a significant part of the renewing of the infrastructure within the United States and other countries of the world. More and more this replacement work is done without cutting trenches to remove the old pipes and replacing with the new pipes. Also the trend is to use polyolefin pipe, especially polyethylene pipe, as the replacement pipe. The present invention is directed to a unique method for removing old pipe and replacing with a polyethylene pipe. In addition, the present invention is directed to a unique system or apparatus including a unique head.
British Gas was a leader in the development of a system to replace gas lines with a system disclosed in U.S. Pat. Nos. 4,505,302; 4,674,914 and 4,693,404. In each of these patents a device is inserted into the existing main and the device, either pivoted cutters or a vibratable breaker device, fractures the main.
Water Research Centre of England have U.S. patents disclosing a system for pipe laying and replacement. U.S. Pat. Nos. 4,634,313 and 4,648,746 both disclose apparatus which have a pneumatically-operated impact device to fracture the existing main.
U.S. Pat. Nos. 4,732,222 and 4,981,181 both disclose an impact device to fracture or break-up the old pipe laid in the ground.
U.S. Pat. No. 4,723,873 discloses a method and apparatus for preparing an existing buried conduit by cooling the conduit or existing main before it is fractured by compressive and impact forces.
U.S. Pat. No. 4,983,071 discloses another device which uses a pneumatically operated impact ram to fracture the existing main.
Each of the foregoing patents disclose a system wherein a impact device is required to fracture the existing main. However, these systems using high impact forces to fracture the main can cause damage to surrounding structures such as buildings and overlying streets or alleyways. Furthermore, the force which will fracture a main in non-compacted ground may be well within the design of the apparatus; however, if the ground is compacted, or concrete surrounds the main, or tree roots or other impediments that can not be seen or foreseen are present, then the fracture of the main may fail to take place.
U.S. Pat. No. 4,507,019 discloses a pipe replacement system which includes an expansion and line replacement mandrel which is inserted into the existing main and a power system which imparts linear movement and rotation to the mandrel. U.S. Pat. No. 4,925,344 discloses another mandrel for the system of the U.S. Pat. No. 4,507,019 patent.
These foregoing patents disclose a system which uses rotation rather than impact to fracture the existing main; however, this system suffers the same deficiencies as the high impact system. When cement is used in a repaired tap or connection to the main, or tree roots or solid rock are in contact with the outside of the main, the system of these patents may not be able to fracture the existing main.
U.S. Pat. No. 4,767,236 discloses a plurality of radially expandable tubular members or liners which engage and then ruptures the portion of the existing pipe adjacent the members or liners.
The system of this patent has no practical application.
U.S. Pat. Nos. 4,886,396 and 4,915,543 disclose a system which includes a shield tunneling machine advanced from a starting shaft, a thrust device for forcing the new concrete pipe into a vacant spot excavated by the machine and advancing the machine, a seal device movable in the existing line ahead of the machine, a discharging device for discharging the excavated substance onto the ground and a temporary watercourse device for permitting sewage to flow through the seal device to a pipeline on the downstream side.
U.S. Pat. No. 4,930,542 discloses a system wherein short-pipes are pressed one after the other intermittently into the pipeline end to end. An expansion piercer or similar broaching tool is pushed through the pipeline at the leading end of the pipe string.
Each of the foregoing patents disclose a system wherein the entire success is dependant on the ability to push short lengths of pipe over a certain distance; however, there is no stability to directing the tunneling machine or expansion piercer tool to follow the path of the old main. The patents assume that the integrity of the main to be replaced will provide the direction of the system; however, mains are replaced due to the lack of integrity of the old mains.
U.S. Pat. No. 5,112,158 discloses a system wherein a head surrounds the outside of the main to be replaced and cuts and breaks the existing line.
The advantages of the method and apparatus of the present invention are that the system is stable in alignment and grade both in the removal of the old main and in the replacement of the polyolefin pipe, the system destroys existing connections and concrete encasements as well as intrusions such as tree roots, the system may use fluid to reduce heat or friction and improve hole stability, and the system can be placed into a ten foot pit. Thus, the present invention not only overcomes the deficiencies of the prior art but has substantial technical advantage over all the known systems.